This invention relates to electrosurgical units, and more particularly to such units with a continuously controllable output voltage whose level remains at a substantially constant value independent of the load.
It has been found that tissue cutting can be accomplished by applying an unmodulated RF carrier to a patient, while coagulation of blood vessels can be achieved by utilizing pulse modulated RF voltage signal. To achieve such electrical signals, there are presently available electrosurgical units which generally provide both an unmodulated and a modulated output voltage, which may be selectively used for tissue cutting or tissue coagulation. The amplitude of the output level of the voltage desired for a cutting or a coagulation procedure varies depending upon the depth of cut, the impedance provided by the patient, and numerous other factors relating to the electrode shape, environment and the particular operating procedure. Accordingly, it is necessary to provide some type of an intensity control whereby the amplitude of the output signal can be controlled. In some electrosurgical units, such intensity control is available only in discrete steps. The electrosurgical unit contains an oscillator with an output tank circuit, and connected to the tank circuit are a number of taps with a rotating dial switch connectable to the individual taps. The voltage level is selected by placing the dial at an appropriate tap. However, because of the many variations in the operating procedures, such discrete steps may not provide sufficient accuracy of control and may cause unwanted problems during its use. A further problem with existing electrosurgical units concerns maintaining the selected output desired. By using the intensity control, the particular output level can be selected for the cutting or coagulation procedure. However, once the output voltage is applied to the patient by means of a hand piece such as a probe or forceps, the patient acts as a load across the output of the electrosurgical unit which causes the output voltage level to drop. Such drops have provided great changes in the desired output level and often necessitate the operator to continuously reset the voltage level as the procedure is carried out. It therefore required the surgeon himself, or an associate, continuously monitor the voltage output level of the electrosurgical unit and continuously make appropriate adjustments as the load on the unit changes. This monitoring requires extra time and skill, and frequently may require the availability of an additional nurse or attendant. Should the voltage output not be monitored, the large variations in the voltage output can cause possible damage or harm to the patient by providing excessive depth of cutting or an improper amount of coagulation.